Re-deployable mobile above ground shelter

ABSTRACT

A protective shelter including an enclosure having at least a floor, at least one sidewall coupled to the floor, a door, and a roof coupled to the at least one sidewall. The protective shelter further includes one or more members coupled to the enclosure that support the protective shelter on a substrate and a resilient grouser attached to at least one of the one or more members and in contact with the substrate.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a divisional of U.S. patent application Ser.No. 13/743,942, which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to protective shelters, and moreparticularly to redeployable mobile aboveground shelters.

2. Description of the Related Art

The construction of storm shelters, safe rooms and blast resistantmodules is well known and thoroughly documented, for example, in FEMA320, Third Edition and FEMA 361, Second Edition, both available from theFederal Emergency Management Agency (FEMA), as well as in ICC/NSSA 2008“Standard for the Design and Construction of Storm Shelters,” publishedjointly by the International Code Council (ICC) and the National StormShelter Association (NSSA) and in Section 6, Wind Loads, of “MinimumDesign Loads for Buildings and Other Structures,” SEI/ASCE 7-05, 2005,ISBN: 0-7844-0809-2, published by the American Society of CivilEngineers. To meet safety standards, conventional shelters requireeither burial below ground or, for one common aboveground shelterdesign, secure fastening of the shelter by numerous metal bolts oradhesives to heavy foundations or concrete “pads”. For pad-anchoredaboveground shelters, the combined weight of the shelter plus itsfoundation or pad is often the primary factor relied upon to resistmovement of the shelter (and thus provide protection of its occupants)during high velocity wind events. In many instances non-residentialaboveground shelters are designed to be permanently installed at onelocation.

If a redeployable or mobile protective shelter is unavailable, personnelthat are temporarily located where severe wind events may occur remainat risk. Those working on oil well drilling rigs, pipeline construction,wind turbine erection, petroleum refineries, compressor station repair,and road construction and repair are examples of personnel at risk. Oneof the challenges of providing severe wind event protection for suchpersonnel is the need for the shelter to be able to be easily, quicklyand inexpensively relocated to different work sites as the crewsfrequently relocate.

Conventional pad-anchored aboveground protective shelters depend almostcompletely upon the total weight of the shelter and its attachedconcrete foundation to resist movement. To a lesser degree, the largewidth of the required concrete foundation also helps the assembly resistoverturning. To resist wind induced overturning, uplift and sliding,some shelters require the use of expensive subterranean concretefootings in addition to the wide width and massive weight of thefoundational pads. Although pre-cast concrete community and industrialshelters are available, their immense weight (approximately 75,000 lbs.or more) requires the use of specially permitted and oversized trucks tohaul them and heavy cranes to lift them into place, which renders theirtemporary redeployment impractical. Some conventional metal shelters canbe unbolted from their heavy concrete bases and moved more easily.However, each new location requires the preparation of another heavyconcrete pad to which the shelter can be bolted. In most instances thecost and inconvenience of pouring of a new pad (and the attendantenvironmental impact of their subsequent demolition and removal) rendersimpracticable the redeployment of a pad-anchored protective shelter fortemporary use.

A second design of aboveground shelter is an “anchored box” thatutilizes one or more exposed wire-lines, chains or cables to providestability in high wind loads to a lightweight metal enclosure, such asan intermodal shipping container. In a typical installation, thesecuring lines are either looped over or attached to the metal enclosureand also anchored to the ground using any of a variety of anchoringdevices, such as helical earth screws, driven piles, or bored holesfilled with cement fitted with “eyes” to which a turnbuckle or othersimilar attachment mechanism can be affixed. Although the anchored boxshelter design affords a greater degree of shelter mobility thanpad-anchored shelter designs, anchored box shelter designs place shelteroccupants at high risk of injury as a result of impact induced failureof the exposed anchoring elements.

SUMMARY OF THE INVENTION

In one embodiment, a protective shelter including an enclosure having atleast a floor, at least one sidewall coupled to the floor, a door, and aroof coupled to the at least one sidewall. The protective shelterfurther includes one or more members coupled to the enclosure thatsupport the protective shelter on a substrate and a resilient grouserattached to at least one of the one or more members and in contact withthe substrate.

Additional embodiments are disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an entry end of a first embodiment of aprotective shelter as seen from above;

FIG. 1B is a bottom plan view of the protective shelter of FIG. 1A;

FIG. 1C is a perspective view of an entry end of the protective shelterof FIG. 1A with its stabilizers retracted, as seen from below;

FIG. 1D is a perspective view of a back end of the protective shelter ofFIG. 1A with its stabilizers extended, as seen from below;

FIG. 2 is an entry end perspective view of a second embodiment of aprotective shelter;

FIG. 3 is an end elevation view of the protective shelter of FIG. 2;

FIG. 4A is a side elevation view of the long sidewall of the protectiveshelter of FIG. 2 illustrating the operation of the air ducts and valvesduring a high velocity wind event;

FIG. 4B is a Cartesian graph of static air pressures versus positionalong the long sidewall of the protective shelter of FIG. 4A during ahigh velocity wind event;

FIG. 5A is a side elevation view of the short sidewall of the protectiveshelter of FIG. 2 illustrating the operation of the air ducts and valvesduring a high velocity wind event;

FIG. 5B is a Cartesian graph of static air pressures versus positionalong the short sidewall of the protective shelter of FIG. 5A during ahigh velocity wind event;

FIGS. 6A-6B respectively depict end and side elevation views of anassembly comprising the protective shelter of FIG. 2 loaded on aroll-off transport;

FIGS. 7A-7D respectively illustrate a top plan, short side elevation,perspective, and long side elevation views of a large capacity thirdembodiment of a protective shelter;

FIGS. 8A-8B respectively depict end and side elevation views of anassembly comprising the protective shelter of FIGS. 7A-7D loaded on aroll-off transport;

FIG. 9 is a perspective view of a fourth embodiment of a protectiveshelter.

FIGS. 10A-10D respectively illustrate an entry-end perspective, shortside elevation, long side elevation, and top plan views of a largecapacity fifth embodiment of a protective shelter;

FIG. 11 is an entry-end perspective view of the protective shelter ofFIGS. 10A-10D illustrating the operation of the air ducts during a highvelocity wind event;

FIG. 12 is a side elevation view of the long sidewall of the protectiveshelter of FIGS. 10A-10D illustrating the operation of the air ductsduring a high velocity wind event;

FIG. 13 illustrates a perspective view of a sixth embodiment of aprotective shelter;

FIG. 14 is an elevation view of the protective shelter of FIG. 13illustrating the operation of the air duct during a high velocity windevent;

FIG. 15 is an elevation view of the protective shelter of FIG. 13 asaugmented with a wind converging structure;

FIGS. 16A and 16B are isometric views of a seventh embodiment of aprotective shelter;

FIG. 17 illustrates, in isolation, an undercarriage rail of a protectiveshelter in combination with a grousing and leveling system; and

FIG. 18 depicts, in isolation, a skirt member of a protective shelter incombination with a grousing and leveling system.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT

In various embodiments, an aboveground protective shelter can utilize anair ducting system and/or retractable stabilizers to resist movement ofthe shelter during a high wind event, such as a tornado, hurricane orexplosion blast. If present, the air ducting system utilizes the reducedair pressure (as described by Bernoulli's principle) that forms inregions above the shelter roof and/or on the shelter sidewall(s) and/oron the leeward shelter wall during a high-velocity wind event toevacuate a substantially enclosed space beneath the shelter floor,reducing the air pressure in the enclosed space to below that of thesurrounding atmospheric pressure and offsetting the aerodynamic liftproduced by the wind accelerating over the shelter roof and around theside walls. The greater the wind velocity over and around the shelter(whether naturally occurring or augmented by some structure), thegreater the holding force created in the enclosed space beneath theshelter, with the holding force in some embodiments always exceeding thelift. The retractable stabilizers, if present and deployed, increase theeffective length and/or width of the protective shelter, increasing themoment arms acting to resist overturning forces produced by a highvelocity wind event (e.g., 250 miles per hour or more). In the same oradditional embodiments, increasing the length and/or width of theenclosed space beneath the shelter (i.e., the “basement”) relative tothe shelter safety cabin floor area proportionately increases theholding force relative to the uplift forces during a high-velocity windevent. Although the vacuum alone is in many embodiments sufficient tohold the shelter against wind forces, the stabilizers can be utilized toprovide redundancy and added safety margin, as can helical or otherstyle earth anchors properly placed.

With reference now to FIG. 1A, there is illustrated a perspective viewof the entry end of a first embodiment of a protective shelter 10 asseen from above. In an exemplary implementation, protective shelter 10includes an enclosure 20 constructed of formed and/or welded, reinforcedsteel (or steel alloy) plate of sufficient strength to protect occupantsand contents of protective shelter 10 from high-velocity wind events,impact and penetration by wind borne debris. In the depicted embodiment,enclosure 20 has a generally rectangular prismatic shape having a floor22, four sidewalls 12, and a roof 14 all formed of reinforced steelplate.

For example, enclosure 20 can be made of welded A36, ¼″ steel plate withreinforcing ribs of sufficient size, placement and design to meet orexceed deflection and penetration limits established by the NationalStorm Shelter Association (NSSA) standard, the Federal EmergencyManagement Agency (FEMA) standards, the American Society of CivilEngineers (ASCE) standards and/or the ICC/NSSA 500 standard. Lesser orgreater material thicknesses, types, and strengths can alternatively beused.

In a preferred embodiment, floor 22 of enclosure 20 is supported by oneor more supports above the underlying substrate (e.g., ground, pavement,rig platform, etc.) when protective shelter 10 is deployed inenvironment 24. For example, in the illustrated embodiment, floor 22 iswelded to and rests upon one or more (e.g., two) undercarriage rails 23(as illustrated in FIGS. 1B-1D) that elevate floor 22 above thesubstrate. In at least some embodiments, undercarriage rails 23 conformto the standard design for roll-off containers, thus allowing theshelter to be loaded and unloaded from a conventional roll-off transporttruck or trailer. For example, according to one conventional standard,protective shelter 10 has two parallel undercarriage rails 23 formed of2″×6″×¼″ (or ⅜″) steel plate that are symmetrically disposed about acentral axis of floor 22 and that are spaced by 36½″. The undercarriagerails are preferably configured (e.g., with openings or spacers placedbetween the rails 23 and the shelter floor 20) so as to not inhibit butto allow the free passage of air from any locale beneath the shelter toany other locale.

Sidewalls 12 are preferably welded to floor 22 to form a substantiallyair-tight connection. One or more security doors 26 (see, e.g., FIGS. 1Aand 1C) are provided in one or more of sidewalls 12 to permit ingressand egress into and out of the interior volume of enclosure 20 and, uponbeing securely closed, to isolate personnel and articles withinenclosure 20 from external threats. Sidewalls 12 may be further providedwith shielded ventilation and pressure relief openings 25 (e.g., in eachof a pair of opposing sidewalls 12) of sufficient size to providesufficient breathing air for the rated number of shelter occupants andpressure relief of the internal space in accordance with the ICC/NSSA500 standard. It is preferable if at least one sidewall 12 has formedtherein a cavity 31 housing a standardized cable connection forattaching the loading winch of a roll-off transport truck or trailer.

In the depicted embodiment, roof 14, which is welded to each ofsidewalls 12, has a curved roof portion 21 along the upper edges of oneor more walls 12 (e.g., the two walls 12 having the greater length).Roof 14 may also have at least one escape hatch 27 to permit egress fromenclosure 20 in the event security door 26 becomes inoperable orotherwise blocked.

Still referring to FIG. 1A and additionally to FIGS. 1B, 1C and 1D,protective shelter 10 may optionally further be equipped with one ormore extendable and retractable stabilizers (outriggers) 28, that whenextended from enclosure 20 (as shown in FIGS. 1A and 1D) increase theeffective width and/or length (and hence moment of inertia) ofprotective shelter 10. In the depicted embodiment, stabilizers 28 arelowered from the retracted position shown in FIGS. 1B-1C to the extendedposition shown in FIGS. 1A and 1D and raised from the extended positionto the retracted position by internally self locking or the more simplestandard hydraulic actuators 29. In alternative embodiment, stabilizers28 can be operated by pneumatic, electrical, mechanical or manualactuators used individually or in combination to raise, lower, test andlock into place all stabilizers during initial deployment of the unitand its subsequent loading for transport and/or redeployment. Whenstabilizers 28 are in the refracted position, as shown in FIGS. 6A-6B,retaining pins 33 may be utilized to secure stabilizers 28, for example,to facilitate transport of protective shelter 10. Exemplary dimensionsfor stabilizers 28 are given in FIG. 3.

Stabilizers 28 may be tipped with force-spreading feet 30 optionallyhaving openings 32 therein to permit installation of optional anchors38. In some embodiments, anchors 38 need only be of such size andmaterial as to withstand the shear forces of the wind against thewindward and leeward sidewalls 12. Anchors 38 can include and beimplemented, for example, with commercially available helical earthanchors or earth screws or even simple metal rods with caps or headssized to prevent being pulled through openings 32. As will beappreciated, the use and holding strength required of anchors 38 toresist sliding and overturning of protective shelter 10 will varybetween embodiments and between installation conditions. Thus, forheavier embodiments (e.g., 20,000 lbs.) or for dense compacted claysoils, shorter anchors 38 exhibiting less holding strength can beemployed. For lighter embodiments (e.g., 12,000 lbs.) or for sandy orloamy soils, longer anchors 38 exhibiting greater holding strength arepreferably employed.

Stabilizers 28 can be used to field prove the holding strength of theprotective shelter 10 and therefore verify that a particularinstallation of protective shelter 10 can withstand the design windspeed. As an initial step, accurate calculations of the overturning anduplift forces produced on protective shelter 10 by a wind of the ratedspeed (e.g., 250 mph) are made, for example, utilizing the Wind Loads onStructures software commercially available from Standards Design Group,Inc. (SDG) of Lubbock, Tex. Hydraulic actuators 29 can then be used toattempt to pull out the anchors 38. If, during this process, thehydraulic pressure reaches a predetermined level (determined, forexample, by the hydraulic cylinder diameter, length of stabilizer 28,and the weight of protective shelter 10) corresponding to the forceexerted on protective shelter 10 by a wind of rated speed (or exceedsthat force by some desirable safety factor) without withdrawingcompromising the anchor(s) 38, then the installation of protectiveshelter 10 is guaranteed to withstand a wind of rated speed.

Although virtually any shape of enclosure 20 can be employed, thepresently preferred shapes and sizes fall within state and federalDepartment of Transportation (DOT) height, width, length and weightlimits for non-permitted loads on public roadways. For example, onepreferred shape is a rectangular prism that, due to its geometry,affords maximum refuge space for occupants, and that, when loaded on itstransport device, has a height, width, length and weight that do notexceed DOT limits. Alternatively, a vertical cylindrical shape (with anyshape or style of roof) can be employed; however, the floor area (andhence occupancy rating) for a cylindrical design is less than that of arectangular prism having a minimum sidewall length at least equal to thediameter of the cylinder. An exemplary protective shelter 90 including acylindrical enclosure with a substantially flat roof 14 is depicted inFIG. 9. Another exemplary protective shelter 130 including a cylindricalenclosure with a substantially domed roof 1314 is depicted in FIGS. 13and 14.

The height of enclosure 20 can also vary between embodiments, withshorter heights generally being preferred because the overturning forceon the windward wall varies with the square of the height if all otherfactors remain constant. A typical height of enclosure 20 is between 72and 96 inches. Although a cylindrical shelter has the disadvantage ofless available floor area within DOT permissible limits, a cylindricalshelter has a significantly lower drag coefficient than a flat-walledshelter, resulting in proportionately lower sliding and overturningforces being induced by a given wind speed (e.g., 250 mph).

It should be understood that virtually any shape and style of roof(e.g., flat, domed, round, parapet, hip, gable, mansard, etc.) can beutilized in the various embodiments of the disclosed protective shelter.However, a roof having inwardly sloping or convexly curved outer edgeson at least two sides and a flat central portion is one of a number ofpreferred embodiments. Such a design is one preferred embodiment becausethe net uplift created by wind passing over enclosure 20 having such aroof design is generally less than those having alternative roofdesigns. Furthermore, such a roof design creates a region of lowpressure concentrated along the beginning of flat portion of thewindward roof edge. In other preferred embodiments, a roof havinginwardly sloping or convexly curved outer edges on at least two sidesand a curved central portion creates a region of maximum low pressureconcentrated at the apex of the curved/arched central portion along itslongitudinal axis. As discussed further below, the low pressure can bebeneficially redirected by a ducting system beneath the shelter floor toassist in resisting movement of protective shelter 10 by high velocitywinds.

Referring now to FIGS. 2-3, perspective and elevation views of a secondembodiment of a protective shelter 10′ are depicted. As indicated bylike reference numerals, the construction of protective shelter 10′ issubstantially the same as that of protective shelter 10 of FIG. 1.Accordingly, protective shelter 10′ includes an enclosure 20′ includinga floor 22, four sidewalls 12 and a roof 14′ all formed of welded platesteel. Protective shelter 10′ may also optionally have stabilizers 28 aspreviously discussed. Unlike protective shelter 10, protective shelter10′ further includes rigid skirting 34 surrounding the base of sidewalls12 to form a lower substantially enclosed sub-floor region (basement airspace) below floor 22.

It will be appreciated that when a solid object of any shape, such asenclosure 20′, is immersed in a flowing stream of fluid (e.g., a wind),areas of relatively lower and higher pressures are created over all thesurfaces of that object according to Bernoulli's principle. Thesedifferent pressures create static and dynamic forces that can influencethe potential movement of the object.

The safety of protective shelter 10′ is enhanced by leveraging thewind-induced air pressures to substantially offset the uplift andoverturning forces created by high velocity wind passing over and aroundenclosure 20′. The wind-induced air pressures are leveraged byimplementing a plurality of (in this embodiment, four) air ducts 36 thatallow rapid air flow between the substantially enclosed sub-floor regionand the environment 24 above roof 14′. The upper ends of air ducts 36can be either open or partially shielded to prevent penetration bydebris.

Each air duct 36 houses a passively operated unidirectional check valve37, the operation of which is biased by gravity (and can be enhancedwith the aid of a spring) to a closed position and during ahigh-velocity wind event is opened by an air pressure differentialbetween the substantially enclosed sub-floor region and the surroundingenvironment to permit only upward airflow. Thus, in the presence of asufficient air pressure differential, an air duct 36 evacuates air fromthe substantially enclosed sub-floor region to the exterior of enclosure20′ above roof 14′. It should be noted that check valves 37 areillustrated approximately at midpoint of air ducts 36, but mayalternatively be located at any position along air ducts 36 withoutnegatively affecting the intended functioning. It should also be notedthat there is a wide variety of check valve designs and constructionsthat will perform equally well.

The size, number, shape and location of air ducts 36 can vary betweenembodiments. For example, other embodiments may include as few as oneair duct 36 (as shown in FIGS. 13 and 14) or more than four. Thegeometry of air ducts 36 is also not critical. Air ducts 36 can have acircular cross-section (as shown in FIGS. 2-5A and 13-14) or any othercross-sectional shape (e.g., rectangular, as shown in FIGS. 11-12)providing sufficient cross-sectional area to permit rapid evacuation ofthe air beneath the enclosure 20′. It will also be appreciated that airducts 36 can also be disposed external to the interior of enclosure 20′(e.g., incorporated into a sidewall 12 and/or reinforcing componentsthereof or be totally independent of the enclosure 20) to increaseusable interior volume within enclosure 20′. Further, the upper openingsof air ducts 36 may be located anywhere on or near the roof surface oreven the side walls and leeward wall(s), but (for the illustrated roofdesign in FIGS. 1A-1D) are most beneficially located adjacent to each ofthe roof corners where the lowest pressure is generated by wind as itaccelerates across roof 14′.

The disclosed air duct and valve arrangement passively and automaticallyselects the lowest air pressure created by the passage of wind over roof14′ of protective shelter 20′ and utilizes the lowest available airpressure to evacuate air from the substantially enclosed sub-floorregion, such that the air pressure in that substantially enclosedsub-floor air space is reduced to below the surrounding atmosphericpressure. Because the air duct and valve arrangement causes air to becontinually withdrawn from the substantially enclosed sub-floor regionof protective shelter 20′ under high velocity wind conditions, thesubstantially enclosed sub-floor region acts as a “suction cup” tocounter uplift, sliding and overturning forces exerted by high velocitywinds and holds protective shelter 20′ securely to the underlyingsubstrate (e.g., ground). In at least some of the preferred embodiments,the holding force exerted by the low pressure in the substantiallyenclosed sub-floor region is always greater than the uplift forceproduced by the wind passing over roof 14′ (i.e., the greater the windvelocity, the greater the holding force created beneath shelter 20′).This holding force significantly diminishes (and can in some instancescompletely obviate) the need for anchors 38 or other ground pinning toprevent enclosure 20′ from lateral sliding and over turning under highwind conditions.

As best seen in FIG. 3, a semi-rigid or flexible sub-skirt 35, forexample, of a rubber or reinforced propylene material, may optionally beadditionally attached with bolts, plates and/or adhesives to the entireperiphery of the lower edge of the rigid skirt 34. Although an EF-5tornado with winds of 250 mph has been known to last several minutes,the typical duration of a deadly tornado is on the order of 10-30seconds. Blast waves from explosions are of even shorter duration, onthe order of less than a second. Sub-skirt 35, if present, providesgreater conformance to the underlying substrate and serves to reduce thelikelihood of pressure-induced “tunneling” under the rigid skirt 34 ifprotective shelter 10′ is placed on an uneven substrate or loose soilsubject to wind erosion during a short duration wind event. Byconforming to the underlying substrate, sub-skirt 35 can assist inmaintaining a vacuum in the substantially enclosed sub-floor region forthe greatest time period, as discussed further below with reference toFIG. 4A-4B. It should further be appreciated that the sub-skirt 35 canbe formed of rigid metal plate and hinged from the lower periphery ofrigid skirting 34 to permit deployment into contact with the substrate.

Referring now to FIG. 4A, there is depicted an elevation view of thelong sidewall 12 of protective shelter 10′ schematically illustratingthe location and functioning of check valves 37 and air ducts 36 duringa severe wind event. FIG. 4B is a Cartesian graph of the static airpressures at various locations relative to protective shelter 10′ duringthe severe, high-velocity wind event (assumed to be a 250 mph wind).

As shown, wind 39 impacts a windward sidewall 12 of enclosure 20′ anddiverts over roof 14′ and around the sides parallel to the winddirection. As shown in FIG. 4B at point A, the wind produces a positivepressure at the windward sidewall 12 of the enclosure 20′ significantlyabove atmospheric pressure (e.g., on the order of +68 psf). As wind 39is diverted upward to pass over enclosure 20′, wind 39 accelerates, andthe static pressure drops until reaching its lowest value at point Bimmediately after turning direction at the roofline. At point B, the airpressure is on the order of −171 psf. The air pressure steadily risesalong roof 14′ as wind 39 begins to flow parallel to roof 14′. Forexample, the air pressure reaches it local maximum of approximately −82psf at point C. As wind 39 begins its downward flow around the end ofroof 14′ after point C, wind 39 again accelerates, and the static airpressure at point D immediately behind the windward sidewall 12 ofenclosure 20′ drops to a value on the order of −104 psf. Thereafter, theair pressure steadily rises until at some point downstream of enclosure20′ the air pressure again equals the ambient atmospheric pressure.

As shown in FIG. 4A, the upstream check valve 37 housed in the upstreamair duct 36 experiences the lowest of the low pressure regions (e.g.,−171 psf) formed by the flow of wind 39 over enclosure 20′. Check valve37 accordingly opens, and air is evacuated from the substantiallyenclosed sub-floor region of enclosure 20′. Conversely, because thestatic air pressure at the downstream air duct 36 is higher (e.g., −82psf) than at the upstream air duct 36, the pressure differential betweenthe upstream and downstream air ducts 36 (e.g., −171 psf−(−82 psf)=−89psf) causes the downstream check valve 37 to remain closed, thusblocking air from entering substantially enclosed sub-floor region ofenclosure 20′ via the downstream air duct 36. The wind-produced lowpressure averaged over the entire area of roof 14′ (e.g., −130 psf) is ahigher pressure than the vacuum created in the substantially enclosedsub-floor region of enclosure 20′ (e.g., −171 psf) acting over theentire area of floor 22, resulting in a net downward force that, whenoperating in combination with the weight of the shelter (e.g., 12,000lbs.), is more than sufficient to hold enclosure 20′ on the underlyingsubstrate with or, in some embodiments, without the aid of stabilizers28.

With reference now to FIGS. 5A-5B, there are illustrated a sideelevation view and corresponding static air pressure graph for the shortsidewall 12 of protective shelter 10′ schematically illustrating thefunctioning of check valves 37 and air ducts 36 during a severe (e.g.,250 mph) wind event directed against the larger sidewalls. As can beseen by comparison of FIGS. 5A-5B to FIGS. 4A-4B, check valves 37 andair ducts 36 operate the same way when wind 39 strikes a long sidewall12 of protective shelter 10′ as when wind 39 strikes a short sidewall 12of protective shelter 10′. In particular, the upstream check valve 37opens to evacuate the air within the substantially enclosed sub-floorregion, thus creating a vacuum that resists the wind-generated uplift onprotective shelter 10′, while the downstream check valve 37 remainsclosed.

Referring now to FIGS. 6A-6B, there are depicted a front end view andleft side view of an exemplary protective shelter 10′ ready fortransport on a standardized roll-off container transport 60. In thedepicted embodiment, the roll-off container transport is a conventionalroll-off container trailer, such as model GN-20 or GN-30 available fromDomatex Inc. of Houston, Tex. In an alternative embodiment, roll-offcontainer transport 60 can be a roll-off container truck. However, theinvention is not limited with regard to the mode of transport that canbe implemented. For example, other types of transport include, but arenot limited to a ballast tractor truck, crane-truck, flat-bed truck,heavy hauler, tilt-bed Landoll with “pop-up” rollers and their similarlyequipped semi-trailers. The assembly comprising protective shelter 10′and roll-off container transport 60 is preferably less than or equal tothe maximum allowed DOT height, width and weight that may be traveledover public roadways without special permits or restrictions.

Currently, the maximum unpermitted DOT-compliant height and width in theUnited States are 168 and 102 inches, respectively. Thus, it ispreferable if the maximum height of the assembly is 168 inches or less(e.g., 161 and 15/16″ as shown) and the maximum width is 102 inches orless. A greater variation in the length of a protective enclosure ispossible while still achieving DOT compliance without securing specialpermits. For example, a shelter with the maximum unpermittedDOT-compliant width can have a length shorter than 7 feet and as greatas 25 feet or longer.

With reference now to FIGS. 7A-7D, there are illustrated top plan, endelevation, perspective and side elevation views, respectively, of athird embodiment of the protective shelter 70. As indicated by likereference numerals, protective shelter 70 is constructed similarly toprotective shelter 10 of FIGS. 1A-1D, but has an enclosure 80 of greaterlength to support a higher occupancy rating (e.g., 25 persons versus12). Because of its greater length, enclosure 80 has a door 26 on eachof its longer sidewalls 12 and omits stabilizers 28 on the shortersidewalls 12.

Referring now to FIGS. 8A-8B, there are depicted a front end view andleft side view of an exemplary protective shelter 70 ready for transporton a roll-off container transport 60. In the depicted embodiment, theroll-off container transport is again a conventional roll-off containertrailer, such as model GN-20 or GN-30 available from Domatex Inc. ofHouston, Tex. In an alternative embodiment, roll-off container transport60 can again be a roll-off container truck. However, the invention isnot limited in regard to the mode of transport that can be implemented.For example, other types of transport include, but are not limited to aballast tractor truck, crane-truck, flat-bed truck, heavy hauler, andtheir similarly equipped semi-trailers such as a Landoll tilt bedtrailer with “pop-up” rollers. As indicated by the exemplary dimensionsgiven in FIGS. 8A-8B, the assembly comprising protective shelter 70 androll-off container transport 60 is preferably less than or equal to themaximum unpermitted DOT height, width and weight that may travel overpublic roadways without special permits or restrictions.

Referring now to FIG. 10A-10D, perspective, front elevation, sideelevation, and top plan views of a fifth embodiment of a protectiveshelter 10″ are depicted. As indicated by like reference numerals, theconstruction of protective shelter 10″ is similar in many respects tothat of protective shelters 10 and 10′ of FIGS. 1A-1D and 2,respectively. Accordingly, protective shelter 10″ includes an enclosure20″ including a floor 22, four sidewalls 12, two doors 26 and a roof14″, which may all be formed of welded plate steel. However, theinvention is not necessarily limited in this regard and otherconstruction materials may be employed. In some embodiments sidewalls 12may be constructed by filling the void between parallel interior andexterior steel plate walls with concrete and/or ballistic ceramic.Moreover, sidewalls 12 may alternatively or additionally be externallyreinforced with a layer of ballistic ceramic. The ballistic ceramic orconcrete not only enhances blast and penetration resistance, but alsomay be utilized as a “ballast” to bring protective shelter 10″ up to adesired overall weight. Sidewalls 12 may be further provided withshielded ventilation and pressure relief openings 25 (e.g., in each of apair of opposing sidewalls 12) of sufficient size to provide prescribedpressure relief and sufficient breathing air for the rated number ofshelter occupants in accordance with the ICC/NSSA 500 standard.

In a preferred embodiment, floor 22 of enclosure 20″ is supported abovethe underlying substrate (e.g., ground, pavement, rig platform, etc.)when protective shelter 10″ is deployed in environment 24. For example,in the illustrated embodiment floor 22 is welded to and rests upon oneor more (e.g., four) undercarriage “skid” rails 42 (as illustrated inFIGS. 10A-10D) that elevate floor 22 above the substrate. Transversebeams 43 are additionally welded to undercarriage rails 42 to providefurther structural support to enclosure 20″. As described above, thecombination of undercarriage rails and transverse beams at the peripheryof floor 22 serves as a rigid skirting to form a lower substantiallyenclosed sub-floor region (air space) 46 below floor 22 (as depicted inFIGS. 10B and 12). The undercarriage rails and transverse beams withinthe enclosed sub-floor region 46 are preferably configured with openingsthere through (e.g., openings 1002 of FIG. 10C) and/or spacers betweenthe rails/beams and floor 22 so as to not inhibit but to allow the freepassage of air from any locale beneath the shelter to any other localewithin the enclosed sub-floor region 46.

Protective shelter 10″ further includes interior partitions formingairspaces communicating between substantially enclosed sub-floor region46 and environment 24. For example, in the depicted embodiment,protective shelter 10″ includes two vertical interior partitions 13(e.g., of plate steel) spaced from and parallel to the two exteriorsidewalls 12 of shorter overall length. The interior partitions furtherinclude a ceiling 15 attached to longer sidewalls 12 and to the tops ofthe two vertical interior partitions 13. Ceiling 15 may be formed, forexample, of plate steel and may have a domed, flat or other shape. Roof14″ and ceiling 15 thus define an attic region (air space) 40 (as bestseen in FIGS. 10B and 10C) between roof 14″ and ceiling 15.

An enclosed doorway 41 additionally extends from each door 26 to theadjacent interior vertical partition 13. Doorways 41 and verticalinterior partitions 13 thus define rectangular interior air ducts 36 oneither side of doorways 41 that communicate between the substantiallyenclosed sub-floor (basement) region 46 and attic region 40.

Roof 14″ further permits airspace communication between attic region 40and environment 24 through an aperture (e.g., exterior vent 45), whichcan be either completely open (as shown) or partially shielded (e.g., bywelded wire screening) to prevent penetration by debris. In the depictedembodiment in which protective shelter 10″ has a dome-shaped roofline,exterior vent 45 is disposed at the apex of roof 14″, thus harnessingthe region of lowest pressure created along the apex of the roofline bythe Bernoulli effect to provide vacuum-assisted resistance to uplift,sliding and overturning forces as described earlier with respect to thesecond and third embodiments (FIGS. 2-5B). It should be noted thatbecause exterior vent 45 is located at the region of lowest pressure, novalving in interior air ducts 36 is required.

Although not specifically illustrated in FIGS. 10A-10D, it should beappreciated that protective shelter 10″ may optionally be equipped withstabilizers 28 and feet 30 and/or a semi-rigid or flexible sub-skirt 35as previously described, for example, with reference to FIGS. 1A-3. Asdescribed above, these additional features may be employed to increaseresistance to overturning forces and to provide additional safetyfactor. Further, as described above with reference to protectiveshelters 10 and 10′, protective shelter 10″ may also be transported on aroll-off container transport 60, such as a conventional roll-offcontainer trailer or roll-off container truck, or may alternatively betransported by other transport vehicles, including but not limited to aballast tractor truck, crane-truck, flat-bed truck, heavy hauler, andsimilarly equipped suitable semi-trailers.

Referring now to FIG. 11, there is depicted an entry-end perspectiveview of the protective shelter of FIGS. 10A-10D illustrating theoperation of interior air ducts 36 during a high-velocity wind event(e.g., a wind load of 250 mph or greater) directed against a longersidewall 12. As shown, wind 39 impacts a windward longer sidewall 12 ofenclosure 20″ and diverts over roof 14″. As wind 39 is diverted upward,wind 39 accelerates over the top of roof 14″, with the static airpressure consequently dropping to its lowest value at the apex of roof14″ where exterior vent 45 is located.

The disclosed arrangement of exterior vent 45, attic region 40 andinterior air ducts 36 thus passively and automatically selects thelowest air pressure created by the passage of wind 39 over roof 14″ ofprotective shelter 10″and communicates that air pressure withsubstantially enclosed sub-floor region 46, thus evacuating air fromsubstantially enclosed sub-floor region 46 via interior air ducts 36,attic region 40 and exterior vent 45 and reducing the air pressure insubstantially enclosed sub-floor air space 46 to below the averageatmospheric pressure of environment 24. Because the arrangement ofexterior vent 45, attic region 40 and interior air ducts 36 causes air47 to be continually withdrawn from the substantially enclosed sub-floorregion 46 of protective shelter 10″ under high velocity wind conditions,substantially enclosed sub-floor region 46 acts as a “suction cup” tocounter uplift, sliding and overturning forces exerted by high velocitywinds and to hold protective shelter 10″ securely to the underlyingsubstrate.

With reference now to FIG. 12, there is depicted side elevation view ofthe protective shelter of FIGS. 10A-10D illustrating the operation ofinterior air ducts 36, attic region 40 and exterior vent 45 during ahigh-velocity wind event (e.g., a wind of 250 mph or greater) directedagainst the shorter sidewall 12. As can be seen by comparison of FIG. 12to FIG. 11, the arrangement of exterior vent 45, attic region 40 andinterior air ducts 36 provides the same vacuum-assisted resistance touplift, sliding and overturning forces described above when wind 39strikes a shorter sidewall 12 of protective shelter 10″. Because of theshorter length of the end walls relative to the side walls the smallercross sectional area produces proportionately less skid force. Andbecause the lengths of the side walls are greater, the tendency for theshelter to overturn in the longitudinal direction is much less. Thevacuum effect produced when wind is perpendicular to the end walls isalso less, but nonetheless sufficient to prevent sliding, overturningand uplift.

With reference now to FIGS. 13 and 14, there are depicted perspectiveand side views of a sixth embodiment of an exemplary protective shelter130. As indicated by like reference numerals, the construction ofprotective shelter 130 is similar in some respects to that of protectiveshelter 90 of FIG. 9. Accordingly, protective shelter 130 includes anenclosure including a floor 22, cylindrical sidewall 12, and door 26 allformed, for example, of welded plate steel. Protective shelter 130 mayoptionally have stabilizers 28 and feet 30 as previously discussed.

However, unlike protective shelter 90 of FIG. 9, protective shelter 130includes a peripheral skirt that, together with floor 22, defines asubstantially enclosed sub-floor region 46. In addition, in contrast toflat roof 14 depicted in FIG. 9, protective shelter 130 includes asubstantially domed roof 1314 having a single vent 1316 that enablesairspace communication between a substantially enclosed sub-floor region46 underlying floor 22 and environment 24, for example, via a centralduct 36. Similar to exterior vent 45 of FIG. 10, vent 1316 is preferablycentrally located at the apex of roof 1314 (i.e., at the region oflowest pressure created by the Bernoulli effect). As best seen in FIG.14, vent 1316 and duct 36 cooperate during a high wind event to evacuatethe air from substantially enclosed sub-floor region 46 and to providethe vacuum-assisted anchoring described earlier with respect to thesecond, third, and fifth embodiments (FIGS. 2-5B and 10A-12). It shouldbe understood that the omni-directional vent and ducting arrangementillustrated in FIGS. 13-14 (like that depicted in the fifth embodimentillustrated in FIGS. 10A-12) does not require any internal valving toprovide vacuum-assisted anchoring.

Referring now to FIGS. 16A-16B, two isometric views of a seventhembodiment of a protective shelter 1600 are depicted. As best seen inFIG. 16A, which provides a partially exploded view, the construction ofprotective shelter 1600 is similar in many respects to that ofprotective shelter 10″ of FIGS. 10A-10D. In particular, protectiveshelter 1600 includes an enclosure 1602 including a floor 1604, foursidewalls 1606 (three of which are illustrated transparently to permitviewing of interior features), one or more (e.g., two) doors 1608 and aroof 1610 (also illustrated transparently), which may all be formed ofwelded plate steel. However, the invention is not necessarily limited inthis regard and other construction materials may be employed. In thedepicted embodiment, the long sidewalls 1606 and roof 1610 mayoptionally be reinforced by an interior framework including multipleribs 1612, which are reinforced by purlins 1614. As shown, one or moreof sidewalls 1606 (e.g., the sidewalls 1606 including doors 1608) may befurther provided with shielded ventilation and pressure relief openings1612 of sufficient size to provide prescribed pressure relief andsufficient breathing air for the rated number of shelter occupants inaccordance with the ICC/NSSA 500 standard.

In the depicted embodiment, protective shelter 1600 further includes askid 1620 that supports enclosure 1602 above the underlying substrate(e.g., ground, pavement, rig platform, etc.) when protective shelter1600 is deployed in environment 24. Skid 1620 includes two parallelundercarriage rails 1622 (e.g., steel I-beams) coupled by a plurality ofspaced cross-members 1624 welded to undercarriage rails 1622. As shown,the footprint of skid 1620 can optionally be widened beyondundercarriage rails 1622 by the addition of a skirt formed of skirtmembers 1634. Floor 1604 of enclosure 1602 and deck plates 1626 of skid1620 are preferably attached (e.g., welded and/or bolted) to rails 1622and/or skirt members 1634 and rest on their upper horizontal surfaces.

Spanning the interstices between cross-members 1624 (and, if skirtmembers 1634 are present, the additional interstices between the skirtmembers 1634 and undercarriage rails 1622) is a subfloor 1630, which canalso be formed of one or more steel plates. Subfloor 1630 can be weldedto rails 1622 and cross-members 1624 (and if present, to skirt members1634), preferably below the level of the top surfaces of rails 1622 sothat subfloor 1630 and floor 1604 are spaced apart. For example, in oneembodiment best seen in FIG. 16B, subfloor 1630 is welded flush with thelower edges of cross-members 1624, but above the lower horizontalsurfaces of rails 1622. By providing a spacing between subfloor 1630 andfloor 1604, ballast 1632, such as concrete or sand or other suitablematerials, can optionally be installed (e.g., poured) below the level offloor 1604 (i.e., under floor 1604 and/or deck plates 1626) over some orall of subfloor 1630 in order to improve the resistance of protectiveshelter 1600 to movement in high velocity wind events by increasing theweight and lowering the center of gravity of protective shelter 1600.

Further, by installing subfloor 1630 above the level of the lowerhorizontal surfaces of rails 1622, a substantially enclosed sub-floorair space 1634 (or “basement”) is formed that is bounded by theunderlying substrate, subfloor 1630, and the members forming theperimeter of skid 1620 (e.g., undercarriage rails 1622 and/or skirtmembers 1634). In embodiments including skirt members extending thewidth of skid 1620 beyond undercarriage rails 1622, the lengths ofundercarriage rails 1622 within substantially enclosed subfloor airspace 1634 are preferably configured with openings there through (e.g.,as described above with respect to openings 1002 of FIG. 10C) to allowthe free passage of air from any point within the substantially enclosedsubfloor airspace 1634 to any other point within the substantiallyenclosed subfloor airspace 1634. Substantially enclosed sub-floorairspace 1634 is in airflow communication with environment 24 via one ormore (in this embodiment, two) air ducts 1616 (illustrated in partialsection in FIG. 16A), which in the depicted embodiment each extendthrough the interior volume of enclosure 1602 and terminate at arespective exterior vent 1640 in roof 1610. In the depicted embodimentin which enclosure 1602 has a dome-shaped roofline, exterior vents 1640of air ducts 1616 are preferably disposed at or near the apex of roof1610, thus harnessing the region of lowest pressure created along theapex of the roofline by the Bernoulli effect to provide vacuum-assistedresistance to uplift, sliding and overturning forces as describedearlier. It should be noted that because exterior vents 1640 are locatedat or near the region of lowest pressure, no valving is required in airducts 1616. Further, because the volume of substantially enclosedsub-floor airspace 1634 is smaller in embodiments including subfloor1630 than in alternative embodiments in which a subfloor is omitted andthe substantially enclosed sub-floor airspace is bounded by floor 1604,the response time between an incremental increase in wind speed overenclosure 1602 and the corresponding pressure drop (i.e., vacuumresponse) within substantially enclosed sub-floor airspace 1634 isdecreased in embodiments including subfloor 1630.

Although not specifically illustrated in FIGS. 16A-16B, it should beappreciated that protective shelter 1600 may optionally be equipped withstabilizers as previously described, for example, with reference toFIGS. 1A-3. As described above, these additional features may beemployed to increase resistance to overturning forces and to provideadditional safety factor.

Additional safety factor can alternatively or additionally be achievedby anchoring protective shelter 1600 to the underlying substrate withoptional anchors 1640. In the illustrated embodiment, anchors 1640 canbe installed through openings 1644 in the corner plates 1642 disposed atthe corners of skid 1620. Anchors 1640 can be implemented, for example,with commercially available helical earth anchors or earth screws oreven simple metal rods with caps or heads sized to prevent being pulledthrough the openings 1644. As will be appreciated, the use and holdingstrength required of anchors 1640 to resist sliding and overturning ofprotective shelter 1600 will vary between embodiments and betweeninstallation conditions. Thus, for heavier embodiments (e.g., 50,000lbs.) or for dense compacted clay soils, shorter anchors 1640 exhibitingless holding strength can be employed. For lighter embodiments (e.g.,30,000 lbs.) or for sandy or loamy soils, longer anchors 1640 exhibitinggreater holding strength are preferably employed. It can be appreciatedthat such anchors are protected against impact from wind borne debrisand thus not susceptible to being severed as would be the case in the“anchored box” design mentioned earlier.

As described above with reference to protective shelters 10, 10′, and10″, protective shelter 1600 of FIGS. 16A-16B may also be transported ona roll-off container transport 60, such as a conventional roll-offcontainer trailer or roll-off container truck, or may alternatively betransported by other transport vehicles, including but not limited to aballast tractor truck, crane-truck, flat-bed truck, heavy hauler, andsimilarly equipped suitable semi-trailers.

With reference now to FIG. 17, additional safety factor for any of thedisclosed embodiments can be achieved by implementing a resilientgrousing system. In an ideal installation site, the substrate 1700 isperfectly (or nearly perfectly) planar, in which case the members of theprotective shelter defining the substantially enclosed sub-floor region(e.g., skirt members 1634 and/or rails 1622 of the protective shelter1600 of FIGS. 16A-16B) contact the substrate along substantially theirentire lengths, and consequently, provide a seal for the substantiallyenclosed sub-floor region against substrate 1700 that maximizes thepressure differential between the substantially enclosed sub-floorregion and the surrounding environment. In many cases, however,substrate 1700 is not ideal and includes one or more locations 1702 ofrelatively higher altitude and/or one or more locations 1704 ofrelatively lower altitude. Such non-ideal sites can be improved by sitepreparation prior to installation of the protective shelter, forexample, by using a bulldozer to compact and/or level the installationsite. Shaping substrate 1700 to more closely conform to the supports(e.g., rails 1622 and skirt members 1632) of the protective shelterdesirably improves safety factor. However, in many cases, sitepreparation can undesirably increase installation cost, modify thenatural contour of the land, and disturb the existing soil andvegetation present at the installation site.

The additional safety factor obtained by performing site preparation toshape substrate 1700 to more closely conform to the supports of theprotective shelter can alternatively be achieved and/or can be improvedby attaching a resilient grouser 1710 to the underside of each of thesupport members of the protective shelter defining the substantiallyenclosed subfloor region (e.g., skirt members 1634 and/or rails 1622) ofprotective shelter 1600). Resilient grousers 1710, which can be formed,for example, of rubber, foam or a polymer, can be attached to thesupport members of the protective shelter defining the substantiallyenclosed subfloor region, for example, using bolts, adhesive and/orfriction fit. As shown in FIG. 17, a resilient grouser 1710 compressesat locations 1702 of relatively higher altitude and, depending on theselected material, can relax or expand at locations 1704 of relativelylower altitude, reducing or eliminating gaps 1706 between the protectiveshelter 1600 and substrate 1700. Consequently, use of resilient grousers1710 provides greater conformance to the underlying substrate 1700, thusserving to level the protective shelter and to reduce the likelihood ofpressure-induced “tunneling” under the protective shelter in cases inwhich the protective shelter is installed on an uneven substrate 1700 oron loose soil subject to wind erosion induced “tunneling” or“rat-holing” under the skirt during a short duration wind event. Byconforming to underlying substrate 1700, resilient grousers 1710 canassist in maintaining a vacuum in the substantially enclosed subfloorregion for the greatest time period. Further, the material from whichresilient grousers 1710 are made can be selected to increase thecoefficient of friction, further reducing the tendency of the protectiveshelter to slide in the presence of a high velocity wind. For example,in one embodiment in which grousers 1710 are formed of a highlyresilient firm foam, the application of grousers 1710 increases thecoefficient of friction of the protective shelter from a valuesubstantially less than 1.0 (e.g., 0.4) to a value greater than 1.0.Although not specifically illustrated in FIG. 17, it should beappreciated that multiple layers and/or varying numbers and/or lengthsof resilient grousers 1710 can be attached to the supports of theprotective shelter as needed to achieve a desired amount of levelingand/or substrate conformance.

Referring now to FIG. 18, there is depicted an exemplary embodiment of aresilient grousing system in combination with a skirt member of aprotective shelter. In the depicted embodiment, skirt member 1634 ofprotective shelter 1600 of FIGS. 16A-16B is implemented as a C-channelsteel beam (e.g., 10 in×4 in) having an upper flange 1800 and a lowerflange 1802 joined by a web 1804. To enable easy assembly of grouser1810 to skirt member 1634, grouser is formed of a block of highlyresilient foam having a slit 1812 along its length sized to receivetherein a lower flange 1802 of skirt member 1634. Thus, prior toprotective shelter 1600 being unloaded onto the substrate at a job site,grousers 1634 can be installed by mating the lower flanges 1802 of skirtmembers 1634 with slits 1812 of grousers 1810 of appropriate length.Grousers 1810 will then retained in place on skirt members 1634 byfrictional fit until it is desired to remove grousers 1810 (e.g., priorto loading protective shelter 1600 on a truck to move protective shelter1600 to another job site).

As has been described, the use of a convex roof having symmetry about atleast the central longitudinal axis of a protective shelter allows windsfrom either direction (containing a velocity component normal that axis)to create the lowest possible static pressure at the same region on theroof regardless of wind direction. A vent opening, which can be of anyshape and in some embodiments is the only such vent opening, ispreferably located at or near the region of lowest static pressure andis utilized to transfer the low static pressure to the sub-floor region,providing the beneficial vacuum-assisted anchoring.

Although specific representative embodiments are illustrated anddescribed herein, those skilled in the art should appreciate that thedisclosed and many other protective shelter designs can be utilized invarious embodiments. For example, the described vacuum-assistedanchoring will work with virtually any shaped roof profile (e.g., flat,mansard, sloped, domed, gabled, hipped, etc.) and with supporting wallsof any configuration (e.g., square, rectangular, cylindrical, hexagonal,octagonal, irregular, etc. when viewed in plan). The use of vacuumducting enables the lowest static pressure created by the wind to berouted to the basement of the shelter, thus generating the greatestpossible vacuum holding effect. Even a single roof opening with aconnecting duct to the basement will route some level of vacuum to thebasement, thus reducing the net vertical forces on the protectiveshelter.

As various shapes and sizes of protective shelters are considered forspecific implementations and specific wind-resistance ratings, it shouldbe appreciated that appropriate selection of the shapes and sizes of theprotective shelter and its components can serve to enhance thevacuum-assisted anchoring during a high-velocity wind event and toachieve desired levels of resistance to wind loads (e.g., resistance toa 200 mph wind, 250 mph wind, 300 mph wind, etc.). For example,increasing the rise of the roof peak as compared to the eve height ofthe protective shelter maximizes the pressure differential between theaverage ambient air pressure of environment 24 and that at located atvent 45 or 1316. However, the benefits of an increased roof rise aregenerally achieved only as long as the roof rise does not exceed half ofthe width (in the embodiment of FIGS. 10A-10D) or diameter (in the domedroof embodiment of FIG. 13). Further, for a given wind speed, theheavier the protective shelter, the less roof rise is needed to achievecomparable shelter performance. Consequently, in many cases, it may bedesirable to make the protective shelter as heavy as is reasonable(e.g., by the addition of more or heavier steel plate or additionalballistic ceramic ballast) while still permitting the protective shelterto be loaded on a transport, transported to an installation site(preferably without special permitting), installed at the installationsite and reloaded on the transport.

Vacuum-assisted anchoring can be further enhanced by increasing the areaof the substantially enclosed sub-floor region relative to thevertically projected area of the roof of the protective shelter. Doingso increases the vacuum-assisted anchoring force generally in proportionto the ratio of substantially enclosed sub-floor region to thevertically projected roof area. This design enhancement is illustrated,for example, by the fifth shelter embodiment depicted in FIGS. 10A-12,in which the length of substantially enclosed sub-floor region 46exceeds that of longer sidewalls 12.

In addition, vacuum-assisted anchoring can be amplified by implementingstructures to accelerate wind speed near vent opening(s), enabling thewind speed experienced locally at a vent opening to exceed that of theambient wind. Greater wind speed decreases static pressure andstrengthens the vacuum-assisted anchoring effect. Consequently,structures accelerating wind speed near vent opening(s) can create avacuum-assisted anchoring effect much greater than that of the ambientwind speed. Vacuum holding forces can thus be “decoupled” from thatnormally produced by a given wind speed, greatly enhancing the stabilityof a shelter against uplift, sliding and overturning forces in any givenwind environment.

The structure that accelerates wind speed near the vent opening(s) cantake a number of forms. In one example depicted in FIG. 15, thestructure takes the form of a shroud 1500 coupled to a protectiveshelter 130 (as previously described) by spaced apart supports 1502 todefine a converging and diverging passage 1504 between substantiallydomed roof 1314 and shroud 1500. Ideally, the narrowest portion ofpassage 1504 is adjacent to vent opening 1506. By selection of thespacing between shroud 1500 from substantially domed roof 1314, adesired and beneficial decrease in static pressure can be achieved inorder to obtain a desired holding strength for protective shelter 1314.As will be appreciated, a structure that accelerates wind speed nearvent openings can also be applied to other embodiments of the describedprotective structure, including that depicted in FIGS. 10A-10D.

It should also be understood that the roof surface(s) are not the onlylocation on a protective structure at which low static pressures arecreated by a passing wind. Consequently, ducting (with or withoutvalves) can be used to communicate low static pressure to the sub-floorregion from any of various locations of low static pressure around thewalls and/or roof of the protective structure in order to provide atleast some degree of vacuum-assisted anchoring. For example, the leewardwall of a protective structure has relatively lower static pressurescreated by the passing wind. Therefore, a vent opening can be providedon the leeward wall (at any desired height above the underlyingsubstrate) and connected by a valved duct to the sub-floor region inorder to use the lower static pressure on the leeward wall to partiallyoffset the uplift force created by the same wind passing over the roofof the protective structure.

In order to appropriate the lower static pressure available on theleeward wall for wind coming from any direction, a protective structuremay incorporate a vent opening on each wall (or side), with each suchvent opening covered by a flap of a flexible material serving as avalve. With this arrangement, on the windward side of the protectiveshelter, the flap is pressed against the vent opening, preventing thehigh static pressure and any air flow from being transferred to thesub-floor region. On the leeward side, by contrast, the flap valve wouldbe lifted by air being drawn out through the vent opening due to theregional low pressure. Should the static pressure present at the sidewall be lower than that induced on the leeward wall (which is often thecase), then both the windward and the leeward wall flap valves would bepulled shut by the lower pressures induced at the side walls, and theside wall flap valves would be open to communicate the relatively lowstatic pressure to the sub-floor region of the protective structure andto provide vacuum-assisted anchoring.

As has been described, a re-deployable mobile aboveground protectiveshelter is capable of protecting personnel and articles from highvelocity wind events (e.g., winds exceeding 250 mph) and withstandingthe uplifting, sliding and overturning forces generated by such highvelocity wind events. In various embodiments, protective shelters mayinclude:

-   -   An enclosure of a material and construction capable of        protecting occupants and contents from high winds and the impact        of wind borne debris;    -   An elevated floor of the enclosure that isolates the occupied        interior space from the surrounding environment;    -   A peripheral skirt of rigid and/or semi-rigid material defining        a substantially enclosed sub-floor region or air space bounded        by the peripheral skirt, the elevated floor of the enclosure and        the surface upon which the enclosure rests;    -   One or more air ducts (with and/or without unidirectional check        valves) permitting air flow from the substantially enclosed        sub-floor region and the external roof and/or sidewall(s),        windward wall(s), and/or leeward wall(s) regions of the        enclosure;    -   A unidirectional check valve in zero or more of the air duct(s)        permitting only the evacuation of air from the substantially        enclosed sub-floor region and preventing movement of air        downward into the substantially enclosed sub-floor region;    -   At least one protective door for ingress and egress into and out        of the protective shelter;    -   An escape hatch for emergency exit in the event a protective        door is inoperable or otherwise blocked;    -   At least one baffled ventilation opening to provide breathing        air for the rated number of occupants while preventing        penetration by dangerous airborne objects;    -   Pressure relief openings to ensure that structural integrity is        not compromised due to the internal/external pressure        differential created, for example, during the passage of a        tornado;    -   Retractable stabilizers that, when extended, increase the        effective width and/or length of the enclosure to enable it to        better withstand wind-induced overturning forces;    -   Hydraulic, pneumatic, electrical, mechanical or manual actuators        used individually or in combination to raise, lower, test and        lock into place all stabilizers during initial deployment of the        unit and its subsequent loading for transport and/or        redeployment;    -   Standardized attachments, cable connections, undercarriage and        supports allowing for the use of DOT-compliant roll-off        container transport trailers and trucks and facilitating the        economic and rapid loading, transportation, unloading and        deployment of the protective shelter; and/or    -   Removable anchors (such as earth anchors or earth screws) that        optionally can be inserted through stabilizer pads and/or        elsewhere to augment the protective shelter's resistance to        sliding.

While the present invention has been particularly shown as describedwith reference to one or more preferred embodiments, it will beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A protective shelter, comprising: an enclosurehaving at least a floor, at least one sidewall coupled to the floor, adoor, and a roof coupled to the at least one sidewall; one or moremembers coupled to the enclosure that support the protective shelter ona substrate; and a resilient grouser attached to at least one of the oneor more members and in contact with the substrate.
 2. The protectiveshelter of claim 1, wherein the enclosure comprises metal plate.
 3. Theprotective shelter of claim 1, wherein the roof has at least one edgeregion having a decreasing height at points further from a central axisof the enclosure.
 4. The protective shelter of claim 1, and furthercomprising at least one ground anchor coupling the protective shelter tothe substrate.
 5. The protective shelter of claim 1, wherein the one ormore members include multiple rails.
 6. The protective shelter of claim1, wherein: the protective shelter and the substrate bound asubstantially enclosed sub-floor region; the roof includes an aperturelocated proximate a point of low static air pressure during ahigh-velocity wind event; and the protective shelter further includes anair duct providing airflow communication between the substantiallyenclosed sub-floor region and an exterior region of the enclosure viathe aperture.
 7. The protective shelter of claim 6, wherein: theenclosure has an interior volume; and the air duct extends through theinterior volume of the enclosure.
 8. The protective shelter of claim 6,and further comprising a structure coupled to an exterior of theenclosure that increases wind velocity adjacent the aperture.
 9. Theprotective shelter of claim 1, and further comprising a ballast.
 10. Theprotective shelter of claim 9, wherein: the protective shelter includesa subfloor that is spaced from the floor; and a ballast is disposedbetween the subfloor and the floor.
 11. The protective shelter of claim9, wherein the ballast includes concrete.
 12. The protective shelter ofclaim 1, wherein: the protective shelter has a first axis and anorthogonal second axis both parallel to a plane including the floor ofthe enclosure; the protective shelter has a greater first dimensionalong the first axis and a lesser second dimension along the secondaxis; and the protective shelter further includes a first deck sectionextending from a first end of the enclosure along the first axis. 13.The protective shelter of claim 12, and further including a second decksection extending from a second end of the enclosure along the firstaxis.
 14. The protective shelter of claim 12, and further comprisingballast disposed in at least one location in a set including the firstdeck section and the second deck section.
 15. The protective shelter ofclaim 12, wherein the door is disposed at the first end of theenclosure.
 16. The protective shelter of claim 12, wherein the one ormore members include multiple rails extending along the first axis. 17.The protective shelter of claim 12, and further comprising ballastdisposed in the first deck section.
 18. The protective shelter of claim17, wherein the ballast includes concrete.
 19. The protective shelter ofclaim 1, wherein the at least one sidewall comprises a substantiallycylindrical sidewall.
 20. An assembly, comprising: protective shelter inaccordance with claim 1; and a transport bearing the protective shelter.